HOW THOUSANDS OF SATELITES KEEP THEMSELVES FROM COLLIDING WITH EACH OTHER?

SpaceX seem to have a solution to this. They have 5,400 of a licenced 12,000 Starlink satellites in orbit, in 3 or 4 narrow ranges of altitudes.

Shells are a nominal 10 km different in altitude.

Maybe they arrange for the crossings to be at say a 1 km altitude difference.

—

I wonder about the popular sun synchronous orbits, typically at high inclinations, and very specific altitudes, crossing near the poles.

They are populated by a variety of satellites managed by scores of different organisations. They may leave it to chance.

PS.
Space is big, and orbits are long, so the chances of collision, even between orbits that exactly intersect is v small. All radar visible objects, including debris, are tracked to predict near collisions (coming within a few km of another). The managers of those objects are informed of the potential collision, and if they can adjust orbit, one or both will do so.

The Starlink satellites make many thousands of collision avoidance moves a year. Many, maybe most, are avoiding debris or non-Starlink satellites. I expect Starlink is managed to avoid near collisions between Starlink satellites, to conserve propellant needed to avoid uncontrolled debris.